This invention relates to a plate holding roller particularly for flexographic printing applications.
It is a known fact that plate holding rollers of this type have been formed, in their outer shrouds, with a longitudinal groove which accommodates known locking devices for securing the ends of the printing plates, wrapped around the roller circumference.
Also known is that, in general, each roller is to accommodate two discrete plates laid adjacently each other. With the aid of conventional securing means, such as spring or camming means no further discussed herein, the two adjacent plates are secured with one end in the longitudinal groove, and then wrapped around the roller to be again secured with the opposite ends in the groove.
It may be appreciated that with such prior arrangements for securing the ends of adjacent plates, no adjustment ability is afforded in the circumferential direction between the plates. This requires that special care be taken in preparing the plates with photo-mechanical methods to provide precision made plates. Furthermore, alignment holes and pins must be used if the plates are to be brought to mutual register.
However, it is not uncommon for the plates to be imperfectly made, and hence out of register when placed adjacently on a common plate holding roller. This often involves the need for laborious operations, which would be to some extent improvised and not always quite successful, in order to locate the two plates on the roller at such mutual positions as they are in true register. If the margin for error between the plates exceeds a given magnitude, then it becomes necessary to re-make at least one of the plates to remove the error condition. This takes considerable and precious time during the installation of the plates on the plate holding roller, while it is not unusual for the related proof test runs to last more than a couple of hours. This drawback is the more heavily felt where the printing of a daily newspaper is to be started.